Firstly based on a flexural experiment of six STS simply members, this paper reveals force model of STS member and obtains key parameters affecting force of STS member. Moreover, a finite element model of STS member is established to optimize the key structural parameters. Secondly FLAC3D is used to build a three-dimensional model and to analyze effect of excavation order of pilot tunnel, excavation order of upper floor, temporary support, stiffness of pipe roof and step length of pilot tunnel on ground settlement and deformation of pipe roof supporting structure for a subway station combining STS with PBA method. Finally based on the structural characteristic of a subway station, influence of construction step on ground settlement, deformation of pipe roof and pier, initial supporting of pipe roof is analyzed with numerical simulation and in-situ monitoring. The results indicate: different excavation order of pilot tunnel and excavation order of upper floor have more effect on ground settlement; it can significantly reduce ground settlement by decreasing length of horizontal pipe roof and making full use of lateral anti-arch interact; through temporary support is erected, it not only reduces settlement of side span, but also limits vertical deformation of pipe roof; the design of step length is reasonable, and can effectively control ground settlement and stability of excavation face.

1. Introduction

The stress redistribution process induced by underground excavations causes soil movements around excavation face in earth mass and finally reflects on the ground surface. Surface settlements caused by underground excavation probably induce severe damages to adjacent buildings and underground facilities, (Sadaghiani et al., 2010; Anastasopoulos, 2013). However, construction of the subway is mostly planned in the prosperous area of city center, it is very necessary to control the surface settlement in the process of constructing the subway. With comprehensive study of experts and scholars from home and abroad, Some methods forecasting surface settlement are proposed by Peck (1969), O'REILLY M P (1982), Wang and ITA (2007), Novozhenin (2016). Meanwhile large span underground excavation in urban area has some characteristics such as wide span, low overburden, heavy street traffic and complex environments, excavation-induced instability and settlement have become principal concern in the design and construction, (Kivi et al.,2012).

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